As is known in the art, a Cherenkov detector is a particle detector using the mass-dependent threshold energy of Cherenkov radiation to allow discrimination between a lighter particle, which does radiate, and a heavier particle, which does not radiate. A particle passing through a material at a velocity greater than that at which light can travel through the material emits light in the form of Cherenkov radiation. This light is emitted in a cone about the direction in which the particle is moving. The angle of the cone, θc, is a direct measure of the particle's velocity through the formula
            cos      ⁢                          ⁢              θ        c              =          c      nv        ,where c is the speed of light, and n is the refractive index of the medium.
Gamma radiation or gamma rays refer to electromagnetic radiation of high frequency (very short wavelength) produced by decay of high energy states in atomic nuclei and high energy sub-atomic particle interactions in natural and man-made processes, such as electron-positron annihilation, neutral pion decay, fusion, fission, lightning strike and terrestrial gamma-ray flash, and astronomical sources in which high-energy electrons are produced. These electrons then produce secondary gamma rays by the mechanisms of bremsstrahlung, inverse Compton scattering and synchrotron radiation. Gamma ray events range from production of a single gamma photon in nuclear decay processes, to explosive bursts of gamma rays in the universe.
As a rule of thumb, gamma rays typically have frequencies above 10 exahertz (>1019 Hz), with energies above 100 keV and wavelength less than 10 picometers, i.e., less than the diameter of an atom. Gamma rays from radioactive decay have energies of a few hundred keV, and almost always less than 10 MeV. Energies from astronomical sources can be much higher, ranging over 10 TeV.
Gamma rays and x-rays are typically distinguished by their origin with X-rays emitted by electrons outside the nucleus, and gamma rays emitted by the nucleus. Exceptions include high energy processes other than radioactive decay, which are still referred to as sources of gamma radiation, such as extremely powerful bursts of high-energy radiation known as long duration gamma ray bursts resulting from the collapse of stars called hypernovas.
A variety of Cherenkov detectors are known. For example, glass scintillators for thermal neutron detection use Li-loaded silicate glass or Li-loaded glass fibers for neutron detection. One disadvantage with Li-loaded glass scintillators is that the neutron response is not well distinguishable from the gamma response when there is a high gamma flux.
Cherenkov light is emitted when a charged particle, such as an electron or a positron, moves faster than the speed of light in a medium. Gamma and x rays of sufficient energy can produce Cherenkov light indirectly by liberating electrons from atoms in the medium (Compton scattering and photoelectric effect) and by generating positrons (pair production).
Detection of Cherenkov light is desirable in high-energy physics applications, such as muon detection and very high-energy (>1 GeV) particle detection. Known detectors include ring imaging Cherenkov detectors made with glass gels of various index of refraction butted together and ordered according to index of refraction so that the Cherenkov cone developed in each section of gel is superimposed on all the others to form a ring of light that is indicative of the energy of the particle passing through the assembly.
Other known Cherenkov detectors use water to detect Cherenkov light caused by the interactions of neutrinos with electrons or nucleons. These interactions result in high-energy electrons that produce Cherenkov light.
In another conventional water Cherenkov detector, the water includes a neutron absorbing material. Neutrons passing through the water are captured by the neutron-absorbing material resulting in the emission of prompt gamma rays, which energize electrons to such an extent that the electrons produce Cherenkov light within the water.
U.S. Pat. No. 7,629,588 to Bell at al., which is incorporated herein by references, discloses an activator detector that detects neutrons using Cherenkov light. U.S. Patent Application Publication No. 2010/0265078 of Friedman, which is incorporated herein by reference, discloses a plasma panel based ionizing particle radiation detector.
To detect gamma radiation and perform neutron moderation in a conventional manner requires separate detection systems. While there are known liquid scintillators sensitive to both neutrons and photons, they are difficult to deploy due to toxicity and flammability. For example, most liquid scintillator detectors are xylene-based. Further, liquid scintillators are not scalable and quite expensive.